Although the presenilin (PS) genes have been linked to familial Alzheimer's disease (FAD), little is known about the physiological functions of the PS or the molecules with which they interact. Moreover, even less is known concerning the effects of FAD- linked PS mutations on functions of PS or their impact on amyloidogenesis or the cellular abnormalities characteristic of AD. PS1/PS2 are integral transmembrane proteins homologous to sel-12, a C. elegans protein involved in an intracellular signaling pathway mediated by members of the Notch/lin-12 family of receptors, which play important roles in determining cell fate. Results from preliminary studies suggest that PS mutations may influence APP metabolism to promote the production of highly amyloidgenic A beta molecules. This project is designed to clarify the roles of PD in development and aging and the influence of PS on APP processing, takes advantages of our expertise in gene targeting methods. PS genes will be ablated, and will examine in detail the phenotypes of the PS1/PS2 targeted hetero-and homozygotes at various stages of development and maturity using a variety of ICC, histological, and stereological methods. It is conceivable that the highly homologous PS proteins may exhibit functional redundancies, and mice null for PS1/PS2 may be phenotypically normal. If so, we will breed mice with deleted PS1/PS2 alleles to generate progeny that are null for both genes and examine the consequences of the double- null state. Because recent work in C. elegans indicates that mutations in sel-12 suppress gain-of-function mutations in the intracellular receptor lin-12, suggesting that sel-12 may be involved in intracellular signalling pathways dependent on activation of lin-12 receptor, we want to identify molecules that interact directly with PS. The yeast two hybrid system will be used to identify proteins interacting with PS1. In our laboratory, this strategy has been useful in identifying HAP-1, which interacts with huntingin. In concert, these efforts will provide new information concerning the roles of PS in neural developing and identify proteins interacting with wt mutant PS.